A magneto-optical recording medium is capable of rewriting recorded information, has a large storage capacity, and is highly reliable as a recording medium. Thus, it begins to be put to practical use as a computer memory or the like. With increases in the amount of information and downsizing of equipment, however, a demand is growing for even higher density recording/reproducing technologies. To record information on a magneto-optical recording medium, a magnetic modulation method is used which irradiates the magneto-optical recording medium with constant laser light, and simultaneously applies a magnetic field of a polarity corresponding to a recording signal to a heated area of the medium. This method permits overwrite recording, and achieves high density recording, e.g., recording at the shortest mark length of 0.15 .mu.m. An optical modulation recording system for irradiating the medium with light power-modulated in response to recording signals under a constant magnetic field applied has also found practical use.
To reproduce or read record marks recorded at a high density, an optical reproduction resolution or resolving power determined by the spot size or diameter of a reproducing light beam should be given particular attention. For example, it is impossible to discern and reproduce a fine mark with a magnetic domain length of 0.15 .mu.m by the use of reproducing light with a spot diameter of 1 .mu.m. As one of approaches for eliminating this restriction on reproduction resolving power by the optical spot diameter of reproducing light, a proposal has been made for magnetic super-resolution (MSR) as described in the Journal of Magnetics Society of Japan, Vol. 17, Supplement No. S1, pp. 201 (1993). This technique utilizes the phenomenon that when reproducing light is cast on a magneto-optical recording medium, a temperature distribution occurs in a magnetic film within a reproducing light spot. Because of this phenomenon, a magnetic mask is generated in the spot to decrease the effective spot diameter contributing to the reproduction or reading of a signal. The use of this technology can improve reproduction resolving power without reducing the actual reproducing light spot diameter. However, this method makes the effective spot diameter small by the action of the magnetic mask. Thus, the amount of light contributing to a reproduction output decreases, and a reproduction C/N ratio declines accordingly. Consequently, it becomes difficult to obtain a sufficient C/N ratio.
Japanese Patent Application Laid-Open No. 1-143041 discloses a reproducing method for a magneto-optical recording medium, which uses a magneto-optical recording medium having a first magnetic film, a second magnetic film and a third magnetic film connected together magnetically at room temperature, the Curie temperatures ohf the first, second and third magnetic films being T.sub.C1, T.sub.C2 and T.sub.C3, respectively, with T.sub.C2 &gt;room temperature and T.sub.C2 &lt;T.sub.C1, T.sub.C3, the coercivity of the first magnetic film, H.sub.C1, being sufficiently small at a temperature in the vicinity of the Curie temperature T.sub.C2 of the second magnetic film, and the coercivity of the third magnetic film, H.sub.C3, being sufficiently large compared with a required magnetic field in a temperature range from room temperature to a required temperature T.sub.PB higher than T.sub.C2,
whereby the recorded magnetic domains of the first magnetic film are enlarged to perform reproduction. This method utilizes a temperature rise of the medium upon irradiation with reproducing light to cut off the magnetic connection between the first and third magnetic films, and enlarges the magnetic domains of the first magnetic film by a demagnetizing field acting in the recorded magnetic domains in this condition and an externally applied magnetic field. With this technique, the second magnetic film used has a Curie temperature set at a lower value than the temperature of a readout area working during reproduction. The present invention, on the other hand, does not use a magnetic film with such magnetic characteristics. PA1 the auxiliary magnetic film is a magnetic film of at least one layer which transforms from a plane-magnetized film into a perpendicular-magnetized film when exceeding its critical temperature, while the magneto-optical recording film is a perpendicular-magnetized film at a temperature not lower than room temperature; PA1 whereby a larger magnetic domain than the recorded magnetic domain of the magneto-optical recording film can be transferred to the auxiliary magnetic film at the time of reproduction by virtue of the magnetic characteristics of the auxiliary magnetic film. PA1 using as the magneto-optical recording medium a magneto-optical recording medium having a first auxiliary magnetic film and a second auxiliary magnetic film sequentially laminated on a magneto-optical recording film, the first and second auxiliary magnetic films being magnetic films which transform from plane-magnetized films into perpendicular-magnetized films when exceeding their critical temperatures, and the magneto-optical recording film, the first auxiliary magnetic film and the second auxiliary magnetic film having magnetic characteristics such that when the Curie temperatures of the magneto-optical recording film, the first auxiliary magnetic film and the second auxiliary magnetic film are designated as T.sub.C0, T.sub.C1 and T.sub.C2, respectively, and the critical temperatures of the first auxiliary magnetic film and the second auxiliary magnetic film are designated as T.sub.CR1 and T.sub.CR2, respectively, a relationship expressed as room temperature &lt;T.sub.CR2 &lt;T.sub.CR1 &lt;T.sub.C0, T.sub.C1, T.sub.C2 is satisfied; and PA1 irradiating the magneto-optical recording medium with reproducing light which is power-modulated with the same period as a reproduction clock or a period created by the multiplication of an integer (n) and the reproduction clock to reproduce a recorded signal. PA1 using as the magneto-optical recording medium a magneto-optical recording medium having an auxiliary magnetic film on the magneto-optical recording film via a nonmagnetic film, the auxiliary magnetic film transforming from a plane-magnetized film into a perpendicular-magnetized film when exceeding its critical temperature, the magneto-optical recording film and the auxiliary magnetic film having magnetic characteristics such that when the Curie temperatures of the magneto-optical recording film and the auxiliary magnetic film are designated as T.sub.C0 and T.sub.C, respectively, and the critical temperature of the auxiliary magnetic film is designated as T.sub.CR, a relationship expressed as room temperature &lt;T.sub.CR &lt;T.sub.C0, T.sub.C is satisfied; and PA1 irradiating the magneto-optical recording medium with reproducing light which is power-modulated with the same period as a reproduction clock or a period created by the multiplication of an integer (n) and the reproduction clock to reproduce a recorded signal.
It is an object of the present invention to solve the problems with the earlier technologies by a method different from the method described in Japanese Patent Application Laid-Open No. 1-143041, and provide a magneto-optical recording medium which gives reproduced signals at a sufficient C/N ratio even when fine magnetic domains are recorded, as well as a reproducing method for the signals.